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    <title>Document</title>
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    <h3>使用默认坐标的矩形</h3>
    <svg width="200" height="200">"
        <rect x="10" y="10" width="50" height="30" style="stroke:black;fill:none"></rect>
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    <h3>使用明确指定单位的矩形</h3>
    <svg width="200" height="200">
        <rect x="10mm" y="10mm" width="15mm" height="10mm" style="stroke:black;fill:none;"></rect>
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    <h3>指定单位视口和没有指定单位的矩形</h3>
    <svg width="70mm" height="70mm">
        <rect x="10" y="10" width="50" height="30" style="fill:none;stroke:black;"></rect>
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